The present invention relates to an aqueous nickel hydroxide or hydrated nickel oxide paste of the generic type disclosed by German Patent Specification 3,817,826.
For several years, not only secondary batteries but also previously tried and tested alkaline storage batteries have undergone further development for use in electric traction (research and development of 000 systems). "Alkaline batteries for electric road vehicles--technical and economic aspects" (Chem.-Ing.-Tech. 51 (1979), No. 6, pages 583 ff.) describes the requirements imposed on a traction battery, the state of development and technical problems in the case of batteries containing an alkaline electrolyte, as well as the economic aspects. A more recent work by G. Benczur, G. Berger and Haschka entitled "Electrodes with fibrous structure" (Eleckrotechnische Zeitschrift etz, vol. 104 (1983), No. 21, page 1098 ff.) deals, inter alia, with the wide variety of electrode designs such as pocket-type plates, tube-type electrodes, sintered electrodes and fibrous-structure electrodes. The optimum structure and the velocity-determining parameters of transport processes in frequently porous electrodes at high current density are reported on for electrochemical cells designed for energy conversion and storage by, for example, K. Mund ("Investigation of porous electrode structures by means of impedance measurements", Dechema mongraphs, volume 102, VCH Verlagsgessellschaft, 1986, pages 83 ff.). Furthermore, German Auslegeschrift 1,496,352 discloses storage battery electrodes composed of a structure of metallic fibers arranged in parallel. Chem.-Ing.-Tech. 53 (1981), No. 2, pages 109 ff. discloses the further development of a plastic composite electrode for lead storage batteries. Chem.-Ing.-Tech. 51 (1979), No. 6, pages 654 ff. deals with the development of NiOOH electrodes having good load-carrying capacity, high unit-area capacity and metallic fibrous structures. Finally, German Patent Specification 3,817,826 claims a high-flowability aqueous nickel hydroxide paste. The last mentioned reference specifies, inter alia, that the nickel hydroxide has a maximum particle size of 0.04 mm, and three examples specify the largest particle diameter determined with a grindometer in the first case as 23.mu.m, in the second case as 18 .mu.m and in a third example as 20 .mu.m in the paste.
In order to achieve particular properties in the paste for filling the electrodes, the solid particles in the paste have to be given a certain fineness. This is done by grinding the feedstock for producing the paste in a ball mill. The particle-size distribution of the Ni(OH).sub.2 powder used and the particle-size distribution of the solid of a usable paste are advantageously represented in the particle size grid of E. Puffe, as described, for example, in DIN 66 145: "Representation of grain-size or particle-size measurement technology" by W. Batel, Berlin-Gottingen-Heidelbert, Springer-Verlag (1971) and in "Particle-size analysis for professional practice", Issue 23 by W. Alex, B. Koglin and K. Leschonski (Chem.-Ing.-Techn. 46 (1974), No. 1, pages 22 ff.) to Issue 35 (Chem.-Ing.-Techn. 47 (1975), No. 3, pages 97 ff.).
In practice, prior art nickel hydroxide pastes have not always proved suitable for filling electrode frameworks, in particular for the vibration filling of fibrous-structure and foam-structure electrode frameworks.
The object of the present invention is therefore to provide a satisfactorily reproducible aqueous nickel hydroxide or hydrated nickel oxide paste for vibration filling fibrous-structure and foam-structure electrode frameworks with which such electrode frameworks can be rapidly and economically produced.
A further object of the invention is to achieve in one operation a uniform constant filling per unit volume of the framework over the entire pore volume of the electrode framework with a degree of filling with moist active material of 94 to 100%. Yet another object is to minimize the necessary technical comminution work relating to the solid particles in the production of the paste.
These and other objects and advantages are achieved, according to the invention, with a nickel hydroxide or hydrated nickel oxide paste having the properties set forth and described in detail herein.
Before the invention is explained in greater detail with reference to examples, the following explanatory remarks should also be made in relation to the subject:
The polydisperse total system of the solid particles in the aqueous paste should be understood to mean a so-called particle universe (also described as a population) in the paste, which universe is composed of a multiplicity of individual particles of different sizes and shapes (i.e. polydisperse) and having a fineness and particle-size distribution which is governed by the specific surface of the ground material and the intensity of the chemical and physical process in the production of the individual particles.
The distribution ogive (cumulative screen passage distribution) of the polydisperse total system of the solid particles was determined in practice using a Micromeritics Sedigraph 5000 (particle-size analyzer) by means of an automated conventional particle-size analysis method based on Stokes' law. The distribution ogive determined was plotted in a particle-size grid (distribution grid) according to P. Rosin, E. Rammler, K. Sperling and I. G. Bennett which has been standardized according to DIN 66 145. During this process it emerged that the particle-size distribution of the solid particles in the paste is progressive (i.e., the curve defined by the measure points is concave upward) in the region of small particle sizes. This results in a bending away of the existing RRSB straight line from the x-axis for the particle sizes less than 10 .mu.m which is due to a large fine-particle enrichment. (See DIN 66 145, above.)
In the region relating to particle sizes between 10 and 19 .mu.m, there is straight line having a particle-size parameter (particle-size characteristic value) of d'=7 .mu.m, with an oversize of R=36.79% and a uniformity coefficient of n=1.36. In the case of a particle size for the solid particles of greater than 19 .mu.m, the distribution is degressive (i.e. the curve defined by the measured points in convex upward). This results in a bending away of the RRSB straight line towards the x-axis between 10 and 19 .mu.m, which is due to a coarse particle depletion in the polydisperse total system. The particles in the resultant paste take on various shapes, including a rouding off shape.